1. Technical Field of the Invention
The present invention relates generally to an engine control apparatus designed to find out an actual position of a crankshaft of an engine for use in an engine control task after the engine is cranked, and more particularly to such an engine control apparatus which works to estimate an angular position of the crankshaft at a stop of the engine and use it in determining the position of the crankshaft at a subsequent start of the engine.
2. Background Art
Japanese Patent First Publication No. 2001-90600 (U.S. Pat. No. 6,341,253 B1) teaches an engine control system designed to monitor an output of a crankshaft position sensor produced in synchronization with rotation of a crankshaft of the engine and an output of a camshaft position sensor rotating at the speed of one-half (½) of that of the crankshaft to determine the angular position of the crankshaft in each cycle of the engine and then launch engine control tasks such as fuel ignition control and fuel injection control for the engine.
The crankshaft position sensor is designed to produce a train of pulses having edges which appear in a unit of a given angle of the crankshaft and also produce a non-pulse portion in which, for example, two edges do not appear, when the crankshaft reaches a given reference position. The camshaft position sensor is designed to change between a high and a low level in synchronization with rotation of the camshaft and have the levels different between two adjacent appearances of the non-pulse portion of the output of the crankshaft position sensor. The camshaft position sensor is made of a magnetic resistance element (MRE).
The engine control system works to determine whether the non-pulse portion has appeared at the output of the crankshaft position sensor or not. When such appearance is detected, the engine control system monitors an instantaneous level of the output of the camshaft position sensor to determine the position of the crankshaft. For instance, when the output of the camshaft position sensor is in the high level, the crankshaft is determined to be in a predetermined position X° CA (crank angle). Alternatively, when it is in the low level, the crankshaft is determined to be in a position 360° CA after the position X° CA. The engine control system works to measure an edge-to-edge interval of the output of the crankshaft position sensor and determines that the non-pulse portion has appeared when a ratio of a current value of the edge-to-edge interval to a previous one is greater than a predetermined value.
Japanese Patent First Publication No. 5-187291 discloses a crankshaft position sensor-less system designed to find the position of the crankshaft and the speed of the engine only using the output of the camshaft position sensor. This type of system, however, consumes the time equivalent to a few turns of the crankshaft between the beginning of engine cranking and the time when the non-pulse portion of the crankshaft position sensor is detected to determine the position of the crankshaft. This results in a delay in launching fuel ignition and fuel injection control tasks for the engine or causes the fuel leaking out of fuel injectors or unburned air-fuel mixture staying within an intake pipe of the engine to be discharged as it is as harmful emissions before start-up of the engine. In order to meet emission regulations tightened in recent years, it is essential to burn out the fuel substantially simultaneously with start-up of the engine by the engine starter to avoid the discharge of the air-fuel mixture to the exhaust pipe as it is.
In order to improve the startability of and the exhaust emissions from the engine, U.S. Pat. No. 5,595,161 teaches an engine control system designed to evaluate outputs of the crankshaft position sensor and the camshaft position sensor at the stop of the engine to estimate the position at which the engine (i.e., the crankshaft) is expected to stop and initiate the engine control task based on the estimate of the stop position of the crankshaft.
Engine control systems of the above type equipped with an stop position estimating function achieves the estimation of the stop position of the crankshaft in accordance with given algorithmic logic. This may, however, result in an error of such estimation depending upon operating conditions of the engine or environmental conditions.
For instance, the lack of warm-up of the engine will result in an increase in viscosity of engine oil, so that the engine has an increased resistance to rotation thereof. This results in an increased possibility that the crankshaft would be reversed in rotation adjust before stopping without exceeding the Top Dead Center (TDC) of one of cylinders of the engine. Such an event may result in a difficulty in estimating the stop position of the crankshaft. The increased resistance to rotation of the engine may cause the waveform, the edge-to-edge interval, or the times of appearance of the edges of the outputs from the crankshaft position sensor and the camshaft position sensor used to estimate the stop position of the crankshaft to be changed from expected ones, thus resulting in an error in estimating the stop position of the crankshaft.
Further, a failure in operation of the crankshaft position sensor or the camshaft position sensor or a disconnection between either of the sensors and the engine control system will also result in an error in estimating the stop position of the crankshaft. Additionally, an undesirable drop in voltage of a storage battery installed in an automotive vehicle arising from aging thereof may also result in undesirable changes in characteristics of the crankshaft position sensor and the camshaft position sensor or a wave-shaping circuit used to shape the waveform of the outputs from the sensors, which will lead to an error in estimating the stop position of the crankshaft.
When it is required to start the engine, initiation of engine control tasks such as the fuel ignition and fuel injection using an erroneous estimate of the stop position of the crankshaft will result in failure in starting the engine or deterioration of exhaust emissions of the engine.